The present invention relates to an electrically controlled force transmitting method and an electrically controlled force transmitting apparatus, wherein transmission of force or transmission of motion such as rotational motion, reciprocal motion, translational motion, etc. is easily controlled by means of an electrical signal. More particularly, this invention relates to a novel method and apparatus for electric control of force transmission, which are applicable to clutches, brakes, shock absorbers, dampers, actuators, and the like.
Various electrically controlled force transmission methods and apparatuses have been proposed. In one known method, use is made of an electro-viscous fluid whose viscosity can be controlled electrically. When a voltage is applied to the electro-viscous fluid, the viscosity of the fluid is increased, thereby a shear stress is induced and a force is transmitted from a drive member to a driven member. Due to this property, the electro-viscous fluid has been utilized in electrically controlled clutches, brakes, shock absorbers, dampers, actuators, and the like. For example, electrically controlled clutches using the electro-viscous fluid have been disclosed in U.S. Pat. No. 2,417,850 and Japanese Patent Application Laid-Open Kokai Sho 57-120,730. A braking apparatus using an electro-viscous fluid has been also disclosed in Japanese Patent Application Laid-Open Kokai Hei 4-63,752.
The electro-viscous fluids, however, have such disadvantages that (1) induced shear stress, which is generated when a voltage is applied, is rather small; (2) a current density during the voltage application is rather high; (3) particles dispersed in the fluids are subject to aggregation and sedimentation due to the gravitational force; and (4) the dispersed particles might cause undesired wear of sealing members such as O-rings in the apparatus which are in contact with the electro-viscous fluid.